1. Field of the Invention
The present invention relates to an antenna device including an antenna coil on a magnetic layer and a communication apparatus including the antenna device.
2. Description of the Related Art
Near field communication (NFC), an example of communication standards that are implemented in an electronic apparatus such as a cellular phone, is a wireless communication technology that allows a reader/writer device and the electronic apparatus to communicate with each other by bringing the electronic apparatus in proximity to the reader/writer device and causing their coils to generate magnetic field coupling to each other. In recent years, an increase in a communication speed by the NFC or the like is required, and a band of an NFC antenna is therefore required to be broadened. Japanese Unexamined Patent Application Publication No. 2001-185939 discloses an antenna coil having a resonance coil that generates magnetic field coupling to a power supply coil and loading a resistance for adjusting a Q-value on the resonance coil so as to try to broaden a band thereof.
However, when the antenna coil disclosed in Japanese Unexamined Patent Application Publication No. 2001-185939 and a device of a communication party are brought close to each other, a coil in the device of the communication party (hereinafter, referred to as party-side coil) generates magnetic field coupling to not only the resonance coil of the antenna coil but also the power supply coil in some cases. In this case, two communication paths including a communication path of the power supply coil→the resonance coil→the party-side coil and a communication path of the power supply coil→the party-side coil are formed. When signals passing through the two communication paths have reverse phases, there arises a problem that the signals are cancelled out by each other and the party-side coil cannot receive the signals. This problem occurs in the same manner even when a transmission and reception relation between the antenna coil and the party-side coil is reversed.